Nuclear reactor core support structure



Oct. 19, 1965 v, SHORT ETAL 3,212,978

NUCLEAR REACTOR CORE SUPPORT STRUCTURE Filed April 18, 1961 6Sheets-Sheet l Fig.l.

WITNESSES: INVENTORS 9 Vincent R. Shon 8 6W Glenn Stevens.

ATTORNEY Oct 1965 v. R. SHORT ETAL 3,212,978

NUCLEAR REACTOR CORE SUPPORT STRUCTURE Filed April 18, 1961 6Sheets-Sheet 2 Oct. 19, 1965 v. R. SHORT ETAL 3,212,978

NUCLEAR REACTOR CORE SUPPORT STRUCTURE Filed April 18. 1961 6Sheets-Sheet .3

Oct. 19, 1965 v. R. SHORT ETAL NUCLEAR REACTOR CORE SUPPORT STRUCTURE 6Sheets-Sheet 4 Filed April 18, 1961 6 7 4 6 2 4 4 I m l. O 9 w w H JP 0w a m H 5 l 4 w 0 9 l\ I 5 B 6 SJ m a, z z m. m 5 m 5 5 1 8 6 w Och 1965v. R. SHORT ETAL NUCLEAR REACTOR CORE SUPPORT STRUCTURE Filed April 18,1961 6 Sheets-Sheet 5 8 .m m F m J w 7 .T m N w w N w J l LX W w R B W Qw. w v m 2 3 w m 8 5 4 8 W B K| IV 3 6 m 9 Oct. 19, 1965 V. R. SHORTETAL NUCLEAR REACTOR CORE SUPPORT STRUCTURE Filed April 18, 1961 U c xIQ 3 Hi 3% -gZO Q E g 222 2 32 Fig.l3.

6 Sheets-Sheet 6 United States Patent 3,212,978 NUCLEAR REACTOR CORESUPPORT STRUCTURE Vincent R. Short, Monroeville, and Glenn Stevens,Turtle Creek, Pa., assignors to Westinghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 18, 1961, Ser.No. 103,911 9 Claims. (Cl. 17633) The present invention is directed toneutronic reactors and, more particularly, to reactors of the typehaving discrete fuel elements supported within a vessel. Morespecifically, the invention is directed to neutronic reactors of theheterogeneous type and to the supporting structure for the fuel elementsthereof.

Heterogeneous neutronic reactors are provided with a core region whereina fissile isotope such as U-235, U-233 and Pu-239 is disposed byproviding a plurality of discrete fuel elements containing such isotope.Moderator material, such as water, is disposed adjacent the fuelelements to permit the thermalizing of neutrons emitted from the fissilematerial. In addition, the moderating material passes adjacent each ofthe fuel elements to conduct heat therefrom. The moderating material isthus caused to act as both a moderator and a coolant. Neutronic reactorsare controlled by providing neutron absorber material, such assilver-indium-cadmium which can be formed desirably as elongated,control elements or rods which are inserted and withdrawn from the coreregion.

As is known, it is necessary to provide a supporting structure withinthe reactor vessel to support the fuel elements and maintain the spacingthereof. The fuel elements are desirably fabricated into assemblies orfuel clusters with each cluster having an upper and a lower extensionformed to position the clusters and to permit the coolant to flowtherethrough. In order to support the fuel clusters, upper and lowercore supporting plates are provided to engage respectively the upper andlower cluster extensions. The core plates are required to be formed soas to position accurately the fuel clusters and support the weightthereof. In accordance with the prior art, such core plates have beenformed of a relatively thick welded sandwich or solid type member orfrom closely spaced parallel sheets of metal providing a hollow area andincluding strengthening means disposed between the sheets.

In the hollow or sandwich type core plates there are substantialdisadvantages. Since a substantial amount of heat is produced and sincea great number of subatomic particles and other radiations, such asgamma rays, are located in a relatively small region, the supportingstructure for the core is in close range of these radiations and issubjected to considerable thermal stresses. Also, since the sandwichtype construction is the primary structural supporting member,particularly in the lower core plate of previous reactors, coolant flowholes must be restricted to increase the rigidity thereof which, inturn, results in fluid pressure losses. Further, this type ofconstruction requires a relatively long time to fabriczTt e due to alarge amount of welding and machining, and is very expensive because ofsuch welding and machining and the possibility of a high scrap rate. Theclosely located but spaced parallel sheet type support plate also hassimilar disadvantages because it too is primarily a supporting structureand must be located close to the core and be thus subjected to intenseheating and neutron bombardment. A thick solid core plate is even moregreatly subjected to extreme gamma heating stresses since this thermalstress varies exponentially as the thickness.

ice

Furthermore, as reactor cores become larger to gain more power output,the abovementioned disadvantages become aggravated.

The present reactor structure overcomes the aforementioned limitationsby providing instead of a relatively thick, solid or sandwich type coreplate, or instead of a pair of closely spaced core plates and connectingstay or flow tubes, single relatively thin upper and lower core plateshaving displaced grid or plate type supporting members attached theretoand employing the adjacent normally present control rod containing tubesfor support. Thus, thermal stresses are kept to a minimum in therelatively thin core plates and are not generally introduced into theguide tube support plate and lower support grid member which are theprimary supporting members for the novel core arrangement. This novelreactor structure eliminates the prior art problems by directing thecore plate load through relatively thin core plates to the presentcontrol rod containing tubes and their attached supporting members. Thesupport members in turn are supported by the vessel walls eitherdirectly or indirectly.

Generally in the reactors of the prior art a second or inner barreloften called an upper core support barrel has been necessary fortransmitting to the vessel wall the dynamic load engendered due to thescramming or falling of control rods. This load first went through aheavy core plate to the upper core support barrel. However, it has beenfound by making the guide tube support plate of a substantially rigidstructure and securing the guide tubes to the guide tube plate that thetubes themselves and guide tube support plate can instead bear theaforementioned dynamic load and thus eliminate the necessity for usingtwo instead of just one barrel above the core and an extra heavy uppercore plate. To accomplish this there is employed a hold-down platesecured to the guide tube plate, the hold-down plate in turn beingengaged by a hold-down ring. The present invention, however, alsocontemplates wing portions secured to the sides of the guide tubeswhereby the wing portions can be either welded, bolted, or in some otherfashion secured to the guide tube support plate directly so as toeliminate the necessity for the extra hold-down plate if that is sodesired. However, When such a hold-down plate is so eliminated and it isstill desired to be able to remove I individual control rod driveshafts, some other means must be provided to accomplish such a purposeif the upper section of the guide tubes are to remain fixed in place.Thus, there is contemplated the use of a removable cover member on thetop of the guide tubes to permit such ready removal or" individual driveshafts. The present invention further contemplates a securing of theguide tubes to the upper core plate which is necessary for the guidetubes to be a substitute for the upper core support barrel.

Further advantages accrue to this novel reactor structure as a result ofsimplified refueling. Prior art arrangements required that the controlrod drive shafts, the guide tubes, and the guide tube support plate allbe removed individually. Then the inner barrel and upper core supportplate were taken out together. While the present structure still permitsindividual drive shafts to be Withdrawn when necessary, it also allowsfor removal of the entire upper core plate supporting structure andassociated components as a single sub-assembly with the control roddrive shafts in place. This advantage becomes more significant in largerreactors as the number of control rods are increased, and as the periodbetween fuel handling operations shortens due to cyclic loadingschedules.

Accordingly, it is an object of this invention to provide a supportingstructure for a reactor core which satisfies the strength requirementsfor such structure but which substantially avoids the necessity of themajor portion of such structure from being in close proximity to thehighly active core elements.

-An object of this invention is to provide a supporting structure forthe internals of a reactor wherein the thermal stresses in suchstructure are substantially reduced. A still further object of thisinvention is to provide a supporting structure for the internals of areactor such that the manufacture, assembly and disassembly, fuelloading, cycling and the like are greatly facilitated.

Another object of the present invention is to provide a core supportingstructure having relatively inexpensive thin supporting plates adjacentthe core with those plates including a substantial number of flow holesso as to minimize fluid pressure losses within the reactor.

Still another object of the present invention is to provide a supportingstructure for a reactor core which is adequately cooled so thatexcessive stresses are not set up to limit the versatility of theoperation of the reactor.

A further object of the present invention is to incorporate otherwisenon-supporting elements of a reactor, such as guide tubes and a guidetube plate, to support a core plate.

An object of this invention is to provide a novel supporting structurefor the upper core support plate of a reactor.

In accord with the above object, another object of the present inventionis to rigidly secure the guide tubes between the upper core plate andthe guide tube support plate whereby the upper core plate is supportedby the guide tubes thus eliminating the necessity for an upper coresupport barrel.

Still another object of the present invention is to fixedly secure theupper guide tubes to the guide tube support plate whereby dynamic loadsfrom scramming of the control rods can be transmitted directly theretorather than to an upper core plate relatively much closer to the core.

A further object of the present invention is to provide a novel mean-sfor securing control rod containing tubes to core support plate and toother supporting components of a reactor.

These and other objects, features, and advantages of the invention willbecome more apparent upon consideration of the following detaileddescription of a novel core supporting structure incorporating variouscomponents constructed in accordance with the principles of theinvention, when taken in connection with the following drawings, inwhich:

FIGURE 1 is a longitudinally-sectioned view of a neutronic reactorconstructed in accordance with the principles ofthe present inventionand taken generally along the reference line II of FIG. 2;

FIG. 2 is a top plan view, partially cross-sectioned, of the reactor ofFIG. 1 taken substantially along the reference line IIII thereof;

FIG. 3 is a partial, cross-sectional view of the core of the reactor ofFIG. 1 taken substantially along the reference line IIIIII thereof;

FIG. 4 is a partial, enlarged view of the upper left portion of thereactor of FIG. 1 including some of the guide tubes and supporting platetherefor and being partially sectioned;

FIG. 5 is a view similar to FIG. 4 but showing a modification of thestructure shown therein;

FIG. 6 is a partial, cross-sectional view of another modification of thestructure shown in FIG. 4;

FIG. 7 is a partial cross-sectional view of a modified form of reactor;

FIG. 8 is an enlarged view of the lower portion of the reactor of FIG. 1and is taken substantially along the reference line VIIIVIII of FIG. 9;

FIG. 9 is a partial, cross-sectional view of the lower reactor portionof FIG. 8 and is taken substantially along the reference line IX-IXthereof;

FIG. 10 is a partial, enlarged, cross-sectional view of the'lowe'rportion "of the reactor as shown in FIG; 8 and taken along the referenceline X-X thereof;

FIG. 11 is a partial bottom plan view of the support grid member andshroud tube assembly shown in FIG. 10 and taken generally along thereference line XI--XI thereof;

' FIG. 12 isa partial, enlarged view of a portion of the reactor asshown in FIG 8 illustrating the inner connection between the shroud tubeand the lower core plate of the reactor; and

FIG. 13 is a partial cross-sectional view of a modified lower portion ofa reactor similar to that shown in FIG. 10.

It can thus be seen that the present description relates to novelsupporting structure for the core and associated elements of a neutronicreactor. This structur employs already existing and necessary componentsof the reactor for providing the proper support for the upper and lowercore supporting plates, which in turn support the core structure,including the fuel elements, of the reactor. More specifically, thisnovel structure fixes the guide tubes to a guide tube support plate andan upper core plate wherein the guide tube support plate is supported bythe vessel and the guide tubes support the upper core plate throughsuspension. Thus, all of the support functions of an inner upper coreplate support barrel used in prior reactors have been transferred to thecontrol rod guide tubes, and the aforesaid inner support barrel has beeneliminated. At the same time, the fabrication of the upper core platehas been simplified by transferring control rod scram loads through theguide tubes directly to the guide tube support plate rather thanhavingthis load absorbed by the upper core plate. As such, the uppercore plate does not bend under these load stresses to damage theadjacent fuel elements when scramrning takes place. Heavy scram loadsare readily taken by the guide tube support plate since it is locatedsome distance away from the core and is not subjected to high intensitygamma heating stresses. The upper core plate can thus be made as asingle ply machined locating plate rather than as a built up weldrnent.The guide tube plate also presents a more advantageous shape forcarrying bending loads since it is only apertured for control rodclearance. The upper core plate, on the other hand, must provideopenings for engaging the fuel assemblies as well as for control rodsand flow passages. The single ply core plate permits machining of guidesurfaces directly in the plate, thus eliminating the need for morecommonly used separate guide blocks. Further, the additional use of aremovable cover used on the end of the guide tubes permits individualremoval of control rod drive shafts where the guide tubes are notreadily detachable from the guide tube support plate. These featuresthus eliminate the need for the more common inner core plate supportbarrel, and if desired, even eliminate the need of a hold-down plate ifthe guide tubes are welded or bolted directly to the guide tube supportplate when it is advantageous to so connect them.

With respect to the lower core supporting plate, this novel reactorstructure'fixes the lower shroud tubes to both the lower core plate anda grid support member wherein the shroud tubes provide support for thelower core plate and in combination with the grid support member and acore supporting barrel provide the primary support for the reactor core.This allows for the lower core plate, now no longer a primary supportingmember, to be relatively thin and substantially perforated and furtherallows the primary support to be a substantial distance from the coreproper. Since the lower grid support member experiences only moderategamma heating and need not be cut-out for large flow holes as is thelower core plate, it is possible to make the structure as stiff asdesired without undue complexity in fabrication. Furthermore, thisinvention permits guide surfaces to be incorporated directly in the coreplate cutouts so that no guide blocks are needed. In the remote locatingof the grid support member, tie rods between the core barrel and thegrid support member can be employled to provide the support for the gridsupport member that would otherwise have to be given by certain ones ofthe shroud tubes interconnected between the grid member and the lowercore plate. In this instance the tie rods would absorb most of thetensional forces and the shroud tubes would bear all of the compressiveforces created by the gravitational force of the core proper. Thus thelower core plate is supported against bending forces over its entirearea. However, it has been found through experimentation that the outergroup of shrOud tubes go generally into tension and share the tensionalload with the tie rods. Because of this it is to be understood that theouter group of shroud tubes can also be used alone instead of the tierods for tensional support, but only at the expense of increased coreplate stresses. Thus, it would only be desirable to eliminate the tierods Where the lowest possible core plate stresses are not necessary.Also, by using tie rods a thinner and cheaper lower core plate can beused because the tie rods are connected directly to the core barrelallowing little deflection of the grid member while the shroud tubes areonly connected to the lower core plate which deflect-s much easier. Withno tie rods the deflection of the peripheral portion of the lower coreplate is carried to the grid member which, in turn, necessitates athicker peripheral portion in the lower core plate to resist suchincreased deflection therein. Furthermore, a dropped rod accident willnot cause any mor than local damage to a single shroud tube because theheavy grid support member distributes the impact load among the tierods. The resilient supports in the grid member also aid in absorbingimpact loads from dropped rods. The supporting structure for the reactorembodied herein is not only substantially less expensive and morepractical, but is also substantially more cfiicient than that of theprior art.

With more particular reference to the drawings, in FIG. 1 there isillustrated a neutronic reactor including a pressure vessel 12 and ahead or cover member 14. The vessel 12 is generally cylindrically shapedhaving a closed bottom and an open top 16 which is onclosed by the covermember 14. The vessel 12 can be formed from any suitable material, suchas steel, having a wall thickness sufficient to withstand internalpressures in the order of 2000 psi. Desirably, a stainless steel lining13 is provided for corrosion resistance purposes. Adjacent the open side16 of the vessel 12 there is pro vidcd an outwardly extending flange 18having a plurality of threaded openings 20 formed therein to receivebolts 22 which extend through registered apertures 24 in the covermember 14. The bolts 22 thus serve to secure the cover member 14 to thevessel 12. Also supported on the cover member are the control rod drivemechanisms (not shown). The control rod drive mechanisms fit into anadapter 15, and the associated control rod drive shafts 17 extendtherebelow. The control rod drive mechanism, adapter, drive shaft, etc.can be of any of the conventional types known in the prior art. For asuitable control rod drive mechanism and associated equipment see Patent2,780,740 entitled Linear Motion Device, issued February 5, 1957, to W.G. Roman et al. The lugs 19 are for purposes of lifting the cover member14 away from the top of the vessel 12 when this is desired.

The vessel 12 is provided with inlet and outlet nozzles 26 and 28,respectively, to which there is secured fluid conduits (not shown) forrespectively conveying coolant into and out of the vessel 12. Theinterior side wall of the vessel 12 is provided with inwardly extendinglugs 32 which can be secured to the pressure vessel 12 by any suitablemeans, as for example by welding. A tubular thermal barrier or shield 34is sized so as to be closely received within the pressure vessel 12 butspaced from the interior side walls thereof to absorb radiation heating.The lower end 36 of the thermal shield 34 is supported by the upwardlyfacing surface of the lugs 32 and is maintained in spaced relation withthe wall of the vessel 12 by means of radial spacers 38 secured to thethermal shield 34 by any suitable means, such as by bolts for example.

An outwardly facing shoulder 49 is disposed on the inner side wall of avessel 12 adjacent the open side 16 thereof. This shoulder 40 receivesthe core supporting structure so that practically the entire load of thereactor core is supported thereby, through suspension. In furtherance ofthis purpose, an upper barrel 42 supports the core barrel 5%), asdescribed later, and is provided with an outwardly extending perpiheralflange 44 which is received and supported by the shoulder 40 of thevessel. The barrel 42 extends downwardly from the flange 44 past thenozzles 26 and 28 and terminates below these tubulations adjacent anupper core plate 46. The outlet nozzles 28 are joined to the interior ofthe barrel 42 through conduit portions 48. That is, the conduit portions48 generally abut against the vessel wall at the nozzles 28 on expandingwith a temperature rise when the reactor is operating.

As stated previously, the core barrel St) is supported at its upper endby the lower end of the upper barrel 42. The upper end of the barrel 50can be coupled to the barrel 42 by means of a clamp 52. The clamp 52,made in several sections as seen in FIG. 3, secures the lower end of thebarrel 42 to the very upper edge of the barrel 50, the 'bottom openingof the barrel 42 being co-extensive with the upper opening of the barrel50. The sections of clamp 52 are then rigidly connected to each other bymeans of bolts 54 or the like. It is also understood that the barrels 42and 50 can be secured together by different means, such as by directlybolting together for example, or can be formed together as a one-piecebarrel. However, while it may be desirous to make them of a onepiececonstruction, for obvious reasons it generally is not practical becausesuch a structure in the bigger reactors is too large to handle andmachine. Suspended from a thlckened portion 56 at the lower end of thebarrel 50 are tie rods 58 and a core support grid 60, which will bedescrlbed in more detail later. Also engaged with the lower end of thebarrel 5% is a lower core plate 62 which will likewise be described inmore detail later.

In the embodiment shown in FIGS. 1 and 4 control rod guide tubes 64 arecomprised of separable upper and lower sleeves 65 and 67, respectively.The lower sleeves 67 are engaged in a plurality of openings 66 in aguide tube support plate or casting 68. The peripheral extremes of theguide tube support plate 68 rest upon the upper flange 44 of the barrel42. It is obvious that the guide tube casting of this invention alsoacts as a guide for the tubes 6 as well as acting as a support therefor.Because of the supporting function of the casting 68 it IS preferred tofix the lower sleeve 67 to the guide tube casting 68 so that the uppercore plate 46 can be supported in tension by the guide tubes 64. It isbecause of this that the guide tubes 64 are fixedly attached at theirlower ends to the upper core plate 46. The guide tubes 64 thus transmitthrough the sleeves 67 the dynamic scram load of the control rodsthrough the flange 44 to the vessel shoulder 4h. The guide tubes notonly support the upper plate 46 but also shield the control rods anddrive shafts contained within the tubes from the water cross flow in theoperating reactor.

One way of so supporting the core plate 46 from the guide tube casting68 is illustrated in general in FIG. 1, and in more detail in FIG. 4.Connected to the lower end and intermediate portions of the shroud tubes64, as by welding for example, are the collars 70 and 72 which containflanges or wings 74 and 76, respectively, for abutting against the upperand lower surfaces of the upper core plate 46 and guide tube castings68, respectively. Slipped over the top of guide tube 64 is a removablecol lar 78 which is adapted to abut against the top surface of the guidetube casting 68. A hold-down plate 80 having apertures 81 generally inregistration with the openings 66 in the guide tube casting 68 is thenslipped over the tops of the sleeves 65 of the guide tubes 64- so thatits lower shoulder portion 82 engages with the top surface of the guidetube casting 68. It is noted that the apertures 81 in the hold-downplate 80 are of such a size that the peripheries thereof engage over thetop surfaces of the collars 78. Registered holes in the holddown plate80, guide tube casting 68, and flanges 76 of the collars 72 permit a nutand bolt assembly 84 to secure these elements together and in turn fixthe guide tube casting 68 to the guide tubes 64. Likewise, registeredholes in the flanges 74 and the upper core plate 46 permit bolts 86 tosecure these elements together.

The sleeves 65 are made separable from the sleeves 67 and are only slipfitted in place so each can be individually removed when it is desiredto withdraw a drive shaft. However, if the upward hydraulic flows are sogreat that they would displace the sleeves 65 from apertures 66 thencollars 78 can be spot-welded or otherwise secured thereto so that thehold-down plate not only secures the guide sleeves 67 to the guide tubesupport plate 68 but also secures the guide sleeves 65 thereto throughcollars 78. This later modification means, however, that the entirehold-down plate must be removed before an individual drive shaft 17 canbe removed unless the top of the sleeves 65 are removable. Thispossibility is discussed later with respect to FIG. 7.

Corresponding to the outer peripheral edge of the holddown plate 80 andthe vessel walls is a hold-down ring 88 which prevents the guide tubecasting 68 from being upwardly movable, until desired. The hold-downring 88 accomplishes this by having a shoulder portion 92 mate with theshoulder 82 of the hold-down plate. These shoulders should always be inproper alignment due to the action of pins 94 which are engaged inregistered apertures 96 and 98 in the flange 44 of the barrel 42 and thehold-down ring 88, respectively. An overlapping portion 102 of thebottom wall of the reactor cover 14 prevents any upward movement of thehold-down ring 88 when the cover is in its closed operative poistion.Thus, the bracing of the reactor cover in its fixed operative positionserves to secure the barrel flange 44, the hold-down ring 88 and, inturn, the guide tubes 64 and guide tube casting 68 in a fixedrelationship to one another whereby the upper core plate 46 is primarilysupported by the guide tube casting 68 by suspension through the columnsor guide tubes 64. It will also be noted that wings 106 weldedly securedto the side walls of the barrel 42 serve as alignment keys for the coreby biting into slots 107 formed in the outer peripheral edge of theupper core plate 46.

An alternate method of supporting the upper core plate 46 is illustratedin FIG. 5. In this modification each guide tube 64 comprises upper andlower abutting sleeves 110 and 112 respectively. The lower sleeve 112has weldedly secured to it a collar 108 which also serves to jointogether with a slip fit the abutting sleeves 110 and 112 of the guidetubes 64. The sleeves 112 are then fixed to the upper core plate 46 andto the guide tube support plate 68 by means of wing portions 114 and 116which are connected respectively to the adjacent guide tube and plate bymeans of welds 118 or the like. Because the guide tubes 64 are secureddirectly to the guide tube support plate 68 and the upper core plate 46there is no need for a hold-down plate for clamping purposes. Because ofthis a hold-down ring 120 can be engaged directly with the guide tubesupport plate 68 by means of mating of shoulder portions 122 and 124 onthe holddown ring and guide tube support plate, respectively. It is ofcourse understood that the guide tubes 64 can be 8 of a one-piece orequivalent construction with the result that an upper section thereofcannot be readily removed. However, this would prevent the removal of asingle drive shaft 17 (FIG. 1) without removing all of the guide tubes64 unless some alternate means, such as illustrated in FIG. 7 andexplained later, are used.

To make sure that the lower ends 126 of guide tubes 64 are located inexactly the proper relationship with respect to apertures 128 in theupper core plate 46, cutout shoulders 125 are provided so that the lowerends 126 can seat on these shoulders and align the openings 128 with theinner tubular portion of the guide tubes 64. Because of this controlrods 90 can move up and down freely through the guide tubes 64 and thecore support plate 46 without interference from protruding edges. It canreadily be seen that in this type of construction not only is the needfor an upper core plate support barrel eliminated, but also eliminatedis the need for accessory equipment such as a hold-down plate. Referenceshould be made to the subsequent description of the modification of FIG.7 for a full understanding of the operability of a non hold-down platemodification. Of course, such elimination of parts renders acorresponding reduction in the cost of materials that would otherwise benecessary to provide an equivalent function.

As illustrated in FIG. 6 another arrangement of a guide tube supportingassembly to employ screw or bolt type assemblies 127 which are used tosecure wings 129 to the guide tube casting 68. However, this arrangementis somewhat different than that of FIG. 5 not only due to the fact thatthe wings 129 are mounted below the guide tube support plate instead ofabove to provide room for an upper collar 131, but also because adifferent configuration of guide tube is employed. Here, instead of thesection 112 of FIG. 5 there are substituted two sections 130 and 132.The upper collar 131 is secured to the section 110, by welds 118 forexample, and slip fits over the top end of the section 130 so as to bereadily removable when it is desired to remove a drive shaft 17 (FIG.1). The reason for this double section is that it is easier to machine ashort section like this to obtain a proper fit with the guide tubecasting 68 than to machine the entire length of a section like section112 of FIG. 5 from heavier walled tubing just to have a shouldered fitas described below.

The section 130 of the guide tube 64 contains an outwardly anddownwardly extending shoulder 134 which serves to seat on the upper endof the section 132 and within notches 136 in the wings 129. By beingengaged between the notches 136 and the upper end of the section 132,the section 130 is securely fixed to the guide tube casting 68, thisshoulder arrangement providing a reinforcement for the bolted connectionformed by the wings 129 and the bolts or screws 127. Instead of wingportions to connect the bottom portion of the guide tube to the uppercore plate 46, a ring type flange 137 is welded, at 118, to the lowerend of the guide tube and this, in turn, is engaged by the bolts 86 tosecure the guide tube 64 to the upper core plate 46. Thus, it canreadily be seen that the modification as illustrated in FIG. 6 alsoprovides the advantages of eliminating the need for an upper inner coreplate support barrel and a hold-down ring as does the modification ofFIG. 5.

The components illustrated in FIG. 7 comprise a broken-out portion froma reactor similar to that illustrated in FIG. 1 only with a modifiedguide tube, guide tube support casting and upper core plate arrangement.Like reference numerals are employed to indicate like parts of thereactors. From this illustration the operability of a non hold-downplate type of assembly and the load bearing effects of the seramming ofcontrol rods on the guide tubes should be more fully understandable.

The guide tube 64 of FIG. 7 comprises two sections, namely a lowersection 138 and an upper section 139. Wings 140 at the end of the lowersection 138 are secured,

by welding or bolting, to the upper core plate 46 so as to providesupport therefore as in the other modifications. Fixedly secured to theupper end of the section 138 is a collar 141 through which bolts 142 canbe used to secure the guide tube section 138 to the bottom of the guidetube casting 68. Thus, the guide tube lower section 133, throughsuspension from the guide tube casting 68, provides the support forupper core plate 46.

However, the guide tube lower section 138 also performs anotherimportant function with respect to the plate 46. That is, it absorbs anyof the dynamic loads which are impressed thereupon due to scramming ofcontrol rods 90 where these loads before were borne by the upper coreplate which often resulted in a distorted surface, so as to cause thecore plate to be projected into interference with the fuel assemblies153 located therebelow. It can be seen from the left-hand guide tube ofFIG. 7 that the control rod 90 is secured to the end of the drive shaft17 through means of an interlocking plate 135; as a result, when thecontrol rod 90 drops from the position shown in the righthand guide tubeof FIG. 7 to that shown in the lefthand guide tube of FIG. 7, it pullsthe drive shaft 17 down with it. This dropping of control rods iscommonly called scrarnming. It can also be seen that in an intermediatesection of the drive shaft 17 is a hydraulic type shock absorber 143,shown in its compressed position in the left-hand guide tube and in itsexpanded position in the right-hand guide tube, so that when the lowerplate 144 of the shock absorber strikes the stop 145 connected to theshroud tube 64 the shock absorber 143 is compressed. Any loadstransmitted by the scramming are thus transferred directly to the lowersection 138 of the guide tube 64, thence to the guide tube casting 68and to the vessel wall. The stop 145 limits the amount of drop which thecontrol rod 90 can take and cooperates with another shock absorberlocated near the other end (see FIGS. and 13) of the dropped control rod91) to absorb the full impact of such dynamic loading. As explainedpreviously with respect to FIGS. 4 to 6, because the guide tube lowersection 138 supports the upper core plate 46 and absorbs any dynamicloading thereon, the upper core plate support barrel usually provided inreactors of this type is eliminated and, in turn, bending stresses onthe upper core plate are eliminated along with any corresponding damagetothe fuel assemblage which may be caused by any bending stresses placedupon the upper core plate 46.

The modification of FIG. 7 primarily differs from the others previouslydescribed in that the upper section 139 is fixedly attached to the guidetube support casting 68 by a collar 146, which in turn is secured to thecasting 68 through a threaded bolt 142. This of course means that thesection 139 cannot be readily removed to permit a drive shaft 17 to betaken out individually unless the bolts 142 holding the collar 146 tothe casting 68 are first removed. It has been found more advantageous tosecure the upper section 139 rigidly to the guide tube casting 68 inthat the upward flow of water or other fluid through the guide tube 64is such that it might lift the upper section 139 out of the aperture 66in the casting 68 if it is not securely fastened thereto. Since theindividual bolts 142 are rather difficult to get at to loosen the sleevewhen it is desirable to remove a single drive shaft 17, some other meansof removing the drive shaft is necessary since the large diameter of thecomponents of the shock absorber 143 cannot pass through an aperture 147in a top cover 148 of the section 139. The cover 148 of this inventionis made readily removable in that it rests on the upper end of thesection 139 by means of an overlapping shoulder 149 and is held theretoby a catch type resilient arm member 150, which is secured at its lowerend 151 to the inner surface of the guide tube section 139 and protrudesthrough an opening in the top cover 148 so that its hooked upper end 152engages the top surface of the cover to keep it in its retainedposition. When it is desired to release the cover 148, the spring ispushed away from its catch engagement with the top cover because theopening through which the upper end 152 protrudes is somewhat largerthan the stem of the catch member 150. A plurality of catch members canbe used, if desired, to secure a single cover 148 on a guide tube. Thus,when it is necessary to remove a single drive shaft 17, the catchmembers 150 are merely moved inwardly towards the center of the cover148 thereby releasing that cover from engagement with the guide tube andthe entire drive shaft and its component parts are lifted through thetop opening in the guide tube upper section 139. It is of courseunderstood that if desired the upper sections 110 of FIGS. 5 and 6similarly could be rigidly connected to the guide tube casting 68 and aremovable top cover such as the cover 148 be employed soas to eliminatethe necessity of using a hold-down plate as illustrated in FIG. 4 topermit individual removal of the drive shafts 17 when desired.

The particular reactor core structure illustrated in FIG. 1 andpartially described thus far does not necessarily form a part of theinstant invention and for a more detailed description of the physicaland nuclear parameters of a typical reactor core, reference can be hadto the detailed description in the patent application of Robert J.Creagan, Serial No. 33,260, filed September 29, 1960, er|- titledNeutronic Reactor and assigned to the same assignee as is the presentinvention.

Generally, however, the reactor core illustrated in FIG. 1 comprises aplurality of encased fuel elements in each cluster 153. Each of the fuelelements are formed by any suitable means well known in the art, as forexample by the use of elongated tubular cladding members formed fromstainless steel and containing stacked uranium dioxide pellets. Some orall of the fuel elements can include uranium dioxide in its natural orsource grade state, that is, with the ratio of uranium 235 to uranium238 equal to 1 to 139. The remainder of the fuel elements can containuranium dioxide in a slightly enriched state wherein the ratio ofuranium 235 to uranium 238 is greater than 1 to 139. The details of thelocation of the slightly enriched elements relative to the naturaluranium elements can be had from the aforementioned copendingapplication. Alternatively, all of the fuel elements can be enriched tothe same or differing degrees.

Each of the fuel elements desirably is hermetically sealed by sealingeach of the stainless steel fuel containing tubes at the ends thereof,for example, by welded oaps. The aforementioned conventional fuelelements and their component parts are not shown in the drawing sincethey are contained within each of the clusters 153. Each cluster 153 hasan outer stainless steel tubular shell 154 for housing the fuel elementsand is provided with a nozzle or other flow conducting supportingassembly 155 disposed at each end thereof. Each nozzle assembly 155 isprovided with a shoulder 156 which is adapted to rest against the coreplates 46 and 62 about the peripheral edges of mating apertures 157.Each nozzle assembly 155 can be cast as a single part or can be formedby welding a group of component parts together, as desired.

It will be appreciated that in this embodiment of the invention, thenozzle structure 155 for each of the clusters 153 is the same at theupper and lower ends thereof. However, this is not a necessaryrequirement. The upper and lower nozzle supporting structures 155 foreach cluster 153 is supported and received by perforations 157 in theupper and lower core plates 46 and 62, respectively, as previouslydescribed. However. a space is generally left between the uppershoulders 156 and the upper core plate 46 during assembly to allow forexpansion of the clusters 153 when the fuel elements are activated.

In viewing FIG. 3, control rod channels 159 are formed between certainof the clusters 153 to permit control rods 90 to be inserted andwithdrawn from a reactor core 160. The particular structural arrangementwhich provides for the control rod channels 159 is Specifically shownand described in the aforementioned copend-ing application, Serial No.33,260. In the present embodiment of the invention, the reactor core 160is adapted to receive a plurality of control rods 90 which, in thisexample, are formed of a cruciform cross-section and which are adaptedto be closely received in the control rod channels 159. Each control rod90 is formed with a neutron absorbing material, as for example theaforesaid alloy, Ag-In-Cd. The control rods 90 are provided withextensions '(not shown) which incorporate fuel elements to complete thepattern in the core where an absorber or control rod 90 is withdrawn.

Surrounding the core clusters 153 is a core baffle 161 havingextremities extending between upper core plate 46 and lower core plate62. Interlocking the baflie 161 to the core barrel 50 are mating prongtype seats 162 which also serve to space the core baflie 161 from thecore barrel wall 50. This in effect is a combining of the barrel and'baffie into an integral structure which requires 'no machining of thebaffle profile after final assembly. Differential pressure is taken bythe round barrel 50 rather than by the form fitting bafile 161. By thisstructure the bathe thickness, and accordingly the overall diameter ofthe" core assembly, is substantially reduced. Also, the fluid coolant isforced to pass through the core and not through the space between thecore barrel 50 and the core baffile 161.

' The'lower support structure is illustrated generally in FIG. 1 andmore specifically in FIGS. 8 to 13. Referring particularly to FIG. 8,the lower supporting arrangement incorporates structural elements havingother purposes in the reactor, such as control rod shroud tubes 163, anduses up otherwise unusued areas of the reactor such as that area in thebottom of the reactor below the lower core plate 62. It can be seen thatthe tie rods 58 are suspended from the thickened portion 56 of the corebarrel 50 by way' of a' screw like engagement through the threaded ends164 of the tie rods. The upper nuts 165 serve to secure'the threadedends 164 in the thickened portion 56. Since the grid plate 60 issuspended from the lower ends of the tie rods 58 and since the shroudtubes 163 are supported at their lower ends on the grid plate 60, it canreadily be seen that generally the shroud tubes 163 serve as columnsupports for the lower core plate 62 withthe grid plate 60 serving asthe primary structural support member therefor. However, as'notedpreviously, the outer rows of shroud tubes 163 actually go intotensionand can serve as the sole tensional support for the grid plate 60if desired. It is mainly the inner shroud tubes 163 which go intocompression to support the weight of the core. Thus, one of the featuresof this invention is that it places the primary structural member awayfrom the high intensity gamma radiation and neu tron bombardment fromthe core assembly so that it can bemade substantially more ruggedwithout sacrificing a corresponding pressure drop in the lower coreplate 62. That is, it can be made heavier and bigger than could acore-plate so that the holes in the casting or grid plate 60 can be maderelatively large so as to minimize any fluid pressure drop when waterpasses through the grid plate 60 into the shroud tubes 163. Also,pressures are decreased in that water entering the core can do so notonly through the bottom of the grid plate 60 but radially through theentire bottom assembly containing the shroud tubes 163. Also, becausethe primary structural member or grid plate 60 is at the lower bottomend of the vessel and away from the gamma radiations it can befabricated, if it is to be a cast peice, with very little finishmachining required so as to substantially reduce the cost thereof. Itcan thus readily be seen that this invention permits the use of a massof structural materials spaced from the core 160 and that the shroudtubes 163 and grid plate 60 minimize bending stresses in the lower coreplate 62.

Because the lower shroud tubes 163 are usually long and extend nearlydown to the bottom of the vessel, this novel arrangement utilizes themfor support by rigidly connecting them between the grid plate 60 and thelower core plate 62. Thus, as mentioned previously, it can be seen thatthe tie rods 58 are in tension while the majority of the shroud tubes163 act as columns and are in compression. If desired, it is alsopossible to eliminate the tie rods 58 and combine the shroud tubes andthe lower core plate 62 and grid plate 60 so that the outer shroud tubesserve as the tension members to support the grid plate 60 in suspensionwhile the inner shroud tubes 163 serve as the compressive elements.ln-this arrangement, the outer row of shroud tubes 163 carry thetensional load to the core barrel 50 instead of the tie rods. This mayrequire some reinforcing of the outer few inches of the lower core platehowever, and on the surface does not appear to be as an etficientmodification as that utilizing the tie rods 58. On the other hand,recent experimental results indicate this can be done by allowing ahigher stress in the core plate.

As mentioned above, the grid plate 60 can be of a casting which canrequire little extra machining. However, the actualm odifications shownin FIGS. 1 and 8 to 11 is a welded construction comprising generallyvertical ribs interconnecting with one another and secured together bymeans of welding and the like. These ribs or beam-s 167 are in a gridpattern and are interconnected by secondary rib or beams 166 extendingdiagonally through the 90 grid pattern. As will be most obvious fromFIGS. 9 to 11, it can be seen that the beams 167 and 166 are notactually joined to one another but are joined to circular sleeves 168which have the main purpose of supporting the lower end of the shroudtubes 163. Welds 170 join the beams 167 and 166 to the sleeves 168.Extending outwardly and welded to the outer row of sleeves 168 are angleirons 172 having apertures 174 therein to receive lower threaded ends176 of the tie rods 58. The tie rods are secured to the angle irons bymeans of the lower nuts 165 so as to provide the necessary tensionalsupport for the grid plate 60.

As seen in FIGS. 10 and 11, the shroud tubes 163 are connected to thegrid sleeves 168 preferably by bolts 178 so that they can be readilyreleasable therefrom. This is accomplished primarily by a narrowed downprotrusion portion 180 which is adapted to fit into-a narrowedconfinement 182 of the sleeves 168, with the protrusion 180 beingthreadedly engaged with end 184 of the shroud tubes 163 to provide forsome adjustment if the lengths of the tubes 163 vary a little. However,it is understood that the protrusion portion 180 can be attached to thelower ends of the tubes 163 permanently by welding or the like if suchadjustment is not necessary or if shimming is to be used instead. Inthis manner, a shoulder 186 of the protrusion 180 rests upon the top ofthe sleeve 168 and the lower portion thereof is engaged by the bolts178, which pass through registered apertures in the bottom of theprotrusion 180 and a securing'plate 188. The securing plate 188 islarger in diameter than the narrowed confinement 182 so that it willengage a shoulder 190 of the sleeve 168 such that the end of the shroudtube is securely fastened to the grid plate 60. Resting on the top ofthe protrusion member 180 is a coil spring member 192, which is held incompression against the top thereof by means of a shroud tube end plate194 which is engaged in an upwardly limited position by means of ashoulder 196 in the shroud tube 163. The purpose of this spring memberis first to facilitate coupling of the drive shaft 17 (FIG. 1) to thecontrol rod90 by raising the uncoupled control rod into a retrievingposition and, second, to absorb part of the impact which is placed uponthe bottom plate 194 in the event a control rod is dropped thereagainstwhen inserted in the shroud tube 163. The movement of plate 194 acts asa hydraulic shock absorber to absorb some of the impact. It is notedthat the plates 194, 188 and protrusion 180 contain apertures 198 whichpermit the flow of water through the shrouds and to prevent stagnantareas of water from forming below the plates 188 and the like.

As seen in FIG. 12, the upper end of the lower shroud tubes 163 aresecured to the lower core plate 62 by means of bolts 200 engaging wingelements 202, which are preferably welded to the sides of the shroudtubes 163 adjacent their upper ends. These bolts 200 are engaged inthreaded openings 204 in the wings which, in turn, are in registrationwith apertures 206 in the core plate 62.

Illustrated in FIG. 13 is a modified shock absorbing form of aninterconnecting assembly between the grid plate 60 and shroud tubes 163comparable to FIG. An interconnecting assembly 208 contains a pair oftubular members 210 and 212 with a flange at one end of each member. Thestem of inner member 212 fits within an aperture 214 in the outer member210. This relationship is such that stem of the member 212 is slidablewithin the stem of the member 210. The assembly 208 contains an opening216 in the stem of its inner member 212 primarily for the same purposesas the opening 198 in the modification of FIG. 10, that is, to allowwater to flow up through the shroud tubes 163. Each shroud tube 163 isthreadedly engaged at 218 around the outer periphery of each member 210so that slightly varying sized shroud tubes 163 can be accommodated bythe interconnecting assemblies 208. Otherwise, if the shroud tubebottoms 163 were welded or otherwise permanently fixed to the topsurface of the grid plate 60 and there was a variance in the length ofadjacent shroud tubes, there woud tend to be undue stresses placed onthe surface of the grid plate 60 or on the shroud tubes 163 which mightcause rupture of either or, at the minimum, make an uneven or unlevelsurface for the fuel assembly supporting or lower core plate 62. Theassembly 208 is fixed to the grid plate 60 by means of a nut 234threadedly engaged with the threads 236 at the lower end of the stem ofthe member 210. The nut 234 in turn engages with a shoulder 238 in theguide plate 60 to fix the assembly 208 to the plate.

Not only do the members 210 and 212 have mating stems but they are alsointerengaged through their flanges. This interengagement takes place bymeans of a plurality of protruding pins 220 fixedly secured to andextending from the flange of the member 212 so as to mate with apertures222 formed in the flange of the member 210. Inserted over each pin 220is a coiled spring 223, which is adapted to absorb impact when theelement 208 is struck on its top surface 224 by a scrammed control rod90. A nut 226 is threadedly engaged with the bottom end of the stem ofthe inner member 212 so as not only to secure the member 212 to theouter member 210, but to provide the proper amount of preloading to thesprings 223. That is, by tightening or loosening the nut 226, the loadon the springs 223 can be properly set.

Also found adjacent the flange and on the stem of the inner member 212is a shoulder 228. The shoulder 228 cooperates with a crushing ring 230,which seats in a cutout 232 in the head of the member 210 such that ifthe dynamic loading of a scramming control rod 90 is so great that thecoil springs 223 cannot absorb the full effect thereof the crush ring230 Will be engaged by the shoulder 228 and as the ring 230 crushes italso absorbs additional energy. Thus, it can readily be seen that thecrush ring 230 serves as a safety feature if the dynamic load from ascrammed control rod is greater than normal, or if the loading on thespring 223 is improper. A further additional safety feature is that evenif the crush ring 230 does not absorb all of the impact the bottom ofthe pins 220 eventually will bear against the top surface of the gridplate 60 to additionally act as a stop if all else fails.

It can be seen that the present invention involves a unique arrangementfor supporting the upper and lower core plates of a neutronic reactor bymeans of incorporating the control rod containing tube elements assupport ing members. Further included is the incorporation of guide tubesupport plate as a main structural core support member as well as theaddition of new elements such as tie rods to give not only a moreeflicient but less costly arrangement for supporting the core elements.

Since it is obvious that the invention can be embodied in other formsand constructions within the spirit and scope thereof, as would beapparent to one skilled in the .art, it is to be understood that theparticular forms shown are but a few of many such embodiments.Accordingly, with various modifications and changes being possible, theinvention is not limited in any way with respect thereto. Moverover, itis to be understood that certain features of the invention can beemployed without a corresponding use of other features thereof.

Accordingly, what is claimed as new is:

1. In a neutronic reactor having an upright annular wall structure, anupright reactor core assembly located in said wall structure, a top coreplate and a bottom core plate forming part of the top and bottomrespectively, said core assembly for positioning fuel element assembliesof said reactor core assembly, elongated tubes located above and belowsaid core assembly and extending upwardly and downwardly therefrom,respectively, and at least some of said tubes being attached at one endto at least one of said plates and at the other end to a support memberlocated adjacent thereto and supported at least indirectly by said wallstructure, said latter tubes providing the basic support for said oneplate and said support member providing the basic support for saidlatter tubes.

2. In a neutronic reactor having an upright annular wall structure, areactor core assembly within said wall structure, a core plate formingpart of said core assembly for at least positioning fuel elementassembly of said reactor core assembly, elongated tubes located in saidreactor and attached at one end to said core plate, said tubes extendingupwardly from said core plate, means attached adjacent the other end ofsaid tubes and supporting said tubes at least indirectly from said wallstructure, said tubes providing the basic support for said core plate,and control rods movable within said tubes.

3. In a neutronic reactor, the combination comprising a vessel, a coreassembly located in said vessel, a guide tube support plate having aplurality of openings therethrough, means supporting said guide platefrom the wall of said vessel and above said core assembly, elongatedguide tubes extending through said guide plate openings, an upper coreplate forming part of said core assembly for positioning elements ofsaid core assembly, and means fixing said guide tubes to said guideplate and said core plate, said guide tubes being the primary supportingelement for said core plate.

4. In a neutronic reactor, the combination comprising a vessel, a coreassembly located in said vessel, a guide tube support plate having aplurality of openings therethrough, means supporting said guide platefrom the wall of said vessel and above said core assembly, elongatedguide tubes extending through said guide plate openings, an upper coreplate forming part of said core assembly for positioning elements ofsaid core assembly, means fixing said guide tubes to said guide plateand said core plate, control rods and connected drive shafts movablewithin said guide tubes, and stop means attached. to the inside of saidguide tubes for stopping said control rods when scramming occurs, saidstop means transferring the dynamic load of the scramming to the guidetubes and guide tube support plate rather than to said core plate.

5. In a neutronic reactor, the combination comprising a vessel, a coreassembly within said vessel, a shoulder provided on the inner side wallof said vessel adjacent the peripheral opening thereof, a cylindricalbarrel having an outwardly extending flange supported by said shoulder,a guide tube plate having a plurality of openings therethrough andhaving an outer extremity supported by said flange, elongated guidetubes extending through said guide plate openings and located above saidcore assembly, a

collar formed around each of said guide tubes and abutting against thetop of said guide plate so as to limit insertion of said guide tubesthrough said guide plate openings, a hold-down plate having a pluralityof openings therein in registration with the openings in said guideplate, said hold-down plate resting on the top of said guide plate andsaid collars, a hold-down ring located around the outer periphery ofsaid hold-down plate and abutting thereagainst, said hold-down ringadapted to be engaged by a cover for said vessel so as to secure saidguide tubes to said guide plate, an upper core plate for positioning andsupporting said core assembly, and means fixing said guide tubes to saidcore plate, said guide tubes thereby providing the primary supportingelement for said core plate.

6. In a neutronic reactor, the combination comprising a vessel, a coreassembly within said vessel, a shoulder provided on the inner side wallof said vessel adjacent the peripheral opening thereof, a cylindricalbarrel having an outwardly extending flange supported by said shoulder,a guide tube plate having a plurality of openings therethroughand'having an outer extremity supported by said flange, elongated guidetubes extending through said guide plate openings, said guide tubesbeing fixed to said guide plate, a hold-down ring extending around theperiphery of said guide plate and engaged therewith, said hold-down ringadapted to be engaged by a cover for said vessel to secure said guidetubes in a fixed position within said vessel, an upper core plateforming part of said core assembly for positioning elements of said coreassembly, the

lower extremity of said guide tubes engaging said core plate and beingfixed thereto, said guide tubes being the primary supporting element forsaid core plate.

7. In a neutronic reactor, the combination comprising i a vessel, a coreassembly within said vessel, a shoulder provided on the inner side wallof said vessel adjacent the peripheral opening thereof, a cylindricalbarrel having an outwardly extending flange supported by said shoulder,a guide tube plate having a plurality of openings therethrough andhaving an outer extremity supported by said flange, elongated guidetubes extending through said guide plate openings, said guide tubesbeing releasably attached to said guide plate, a hold-down ringextending around the periphery of said guide plate and engagedtherewith, said hold-down ring adapted to be engaged by a cover for saidvessel to secure said shroud tubes in a fixed position within saidvessel, an upper core plate forming part of said core assembly forpositioning elements 'of said core' assembly, the lower extremity ofsaid guide tubes engaging said core plate and being releasably attachedthereto, said guide tubes being the primary supporting element for saidcore plate. a 8. In a neutronic reactor, the combination comprising -avessel, a core assembly located in said vessel, a guide tube supportplate having a plurality of openings therethrough, a shoulder formed onthe inner side wall of said vessel, a barrel having an outer peripheralflange engaging said shoulder, the outer extremities of said guide plateresting on the top of said flange, elongated guide tubes Within saidvessel extending through said guide plate openings and secured to saidguide plate, an upper core plate forming part ofsaid core assembly forpositioning elements of said core assembly, means fixing the lower endsof said guide tubes to said upper core plate, and means on the barrelfor positioning the outer'extremities of said core plate, said guidetubes being the primary supporting ele- -ment for said core plate.

9. In a neutronic reactor, the combination comprising a vessel, a coreassembly located in said vessel, a guide tube support plate havingaplurality of openings therethrough and spaced at a sufiicient distanceabove said core assembly so as to reduce substantially the heatingefiects from attendant radiation, means supporting said guide plate fromthe wall of said vessel and above said core assembly, elongated guidetubes extending through said guide plate openings, an upper core plateforming part of said core assembly for positioning elements of said coreassembly, and means of fixing said guide tubes to said guide plate andto said core plate, said guide tubes and 'said guide plate being theprimary supporting means for said core plate.

References Cited by the Examiner UNITED STATES PATENTS 2,848,404 8/58Treshow 17664 2,977,297 3/61 Evans ct al. 17681 2,982,713 5/61 Sankovichet al 176-61 2,986,509 5/61 Duffy 17664 2,990,349 6/61 Roman 17654 XR3,060,111 10/62 Sherman et a1 176-43 XR CARL D. QUARFORTI-I, PrimaryExaminer. REUBEN EPSTEIN, Examiner.

1. IN A NEUTRONIC REACTOR HAVING AN UPRIGHT ANNULAR WALL STRUCTURE, ANUPRIGHT REACTOR CORE ASSEMBLY LOCATED IN SAID WALL STRUCTURE, A TOP COREPLATE AND A BOTTOM CORE PLATE FORMING PART OF THE TOP AND BOTTOMRESPECTIVELY, SAID CORE ASSEMBLY FOR POSITIONING FUEL ELEMENT ASSEMBLIESOF SAID REACTOR CORE ASSEMBLY, ELONGATED TUBES LOCATED ABOVE AND BELOWSAID CORE ASSEMBLY AND ETENDING UPWARDLY AND DOWNWARDLY THEREFROM,RESPECTIVELY, AND AT LEAST SOME OF SAID TUBES BEING ATTACHED AT ONE ENDTO AT